1. Field of the Invention
The present invention generally relates to a surface polishing method and an apparatus thereof which apparatus polishes the surface of a hard brittle material, such as silicon and glass, and a metal material, such as steel and aluminum by using a polishing tool; and in particular, an apparatus that can stably execute a high quality polishing process with high efficiency for a long time. These method and apparatus can be effectively applied to a surface polishing process for a glass product and a surface flattening process for a semiconductor device wafer.
2. Description of the Related Art
In order to flatten the surface of a component made of a hard brittle material such as a silicon wafer and a glass disk, a polishing process is executed by using loose abrasive grains. However, in the process, problems, such as warp, roll, and generation of steps on the surface, are liable to occur, and the problems reduce the accuracy of the polished surface shape.
In order to solve these problems, development of a fixed abrasive grain polishing tool (for example, a grinding stone) which can obtain good finished surface smoothness equal to that obtained by conventional polishing has been actively realized. That is, a highly accurate shape can be obtained by the fixed abrasive grain polishing tool. However, the fixed abrasive grain polishing tool, such as the grinding stone, has various defects. As representative defect examples, there are occurrence of swarf clogging the surface of the grinding stone, dulling of the grinding stone in the polishing process. Consequently, predetermined polishing characteristics cannot be maintained. Therefore, generally, dressing the grinding stone must be executed by a mechanical or an electrical method.
In addition, in order to solve the above problem, for example, in Patent Document 1, as a dressing method for a polishing tape, high pressure cleaning liquid is ejected from a nozzle onto the polishing surface of the polishing tape. The cleaning liquid becomes fog droplets in the air by being ejected at high pressure, the fog droplets crash against the polishing tape, and the polishing swarf clogging the polishing tape is forced out from the polishing tape. However, by this process, the apparatus becomes complex, and a large shock and resulting vibration are received by the polishing tape. Consequently, it is difficult to realize high surface shape accuracy.
Further, in Patent Document 2, a method of polishing an object by supplying loose abrasive grains to a polishing wheel being a fixed abrasive grain polishing tool is disclosed. In this polishing process, instead of performing dressing with a conventional dresser, loose abrasive grains are used together with the fixed abrasive grain polishing tool, and fixed abrasive grains worn down in the polishing wheel are dropped from a binder and clogging of holes is prevented. Further, this document teaches that the loose abrasive grains are sequentially supplied to the parts from which the worn grains are dropped, and high polishing ability can be maintained.
In this method, hastening the dropping of the fixed abrasive grains in the surface layer of the polishing wheel is executed and the parts from which the worn grains are dropped and the hole parts hold the loose abrasive grains. However, there is no difference from a conventional polishing cloth (polishing pad), and it is considered that the mixing effect of the loose abrasive grains with the fixed abrasive grain polishing tool cannot be fully obtained.
For the above reasons, as a result of various research activities, in order to obtain long time polishing life, maintaining high polishing surface quality (scratch-free surface, highly accurate shape), realizing high processing efficiency, it is found that applying the fixed abrasive grains with the loose abrasive grains onto a surface of an object to be processed is effective. That is, in the process, without dropping the fixed abrasive grains from the binder, the tips on the top of the fixed abrasive grains are worn down and flattened, and the generation of fine cutting edges on the fixed abrasive grains is always obtained. Therefore, the mixing effect of the fixed abrasive grains together with the loose abrasive grains on a surface of an object to be processed is always maintained. In addition, because the tips on the top of the fixed abrasive grains are worn down and flattened by the supplied loose abrasive grains, and the commonly-used sophisticated dressing methods are not necessary. That is to say, in the process, there is no need to provide the dressing process that requires profound knowledge and experience.
[Patent Document 1] Japanese Laid-Open Patent Application No. 2004-160628
[Patent Document 2] Japanese Laid-Open Patent Application No. 10-296610